Forming method and means



Dec. 8, 1964 F. J. PESAK 3,150,130

FORMING METHOD AND MEANS Filed Jan. 31, 1961 4 Sheets-Sheet l INVENTOR.

FRANK J. PESAK ATTORN EY Dec. 8, 1964 F. J. PESAK 3,160,130

FORMING METHOD AND MEANS Filed Jan. 51, 1961 4 Sheets-Sheet a FRANK J.PESAK X W w ATTORNEY Dec. 8, 1964 F. J. PESAK 3,160,130

FORMING METHOD AND MEANS Filed Jan. 51, 1961 4 Sheets-Sheet 4 2- 1- I m1 l 13% R m N\ o N 4 a: o

a] g N qo o --N a I "H g 1 m N N N r r N N N no 2 g u. 3

l0 3 &

,3 N N INVENTOR.

FRANK J. PESAK m -xx ATTORN EY RESERVOIR United States Patent 3,16%,139FURMING METHOD AND MEANS Frank .F. Pena-k, Encino, (Kalli, assignor toNorth American Aviation, Inc. Filed Jan. 31, 1961, Ser. No. 86,188 12Claims. (Cl. 1l344) This invention concerns method and apparatus forforming various objects of diverse shapes and materials startinginitially from an elongate workpiece or blank of generally tubular form.More particularly, this inven tion contemplates improved method andapparatus for fabricating a hollow article from a tubular blank orspecimen of deformable material by deforming the material progressivelystarting at or near one end of the blank and proceeding along itslength, and by closely controlling the amount, the rate, and thelocation of deformation of such material by the application of forcesthereon.

The invention disclosed herein is applicable to the fabrication of anyarticle which can be formed by expansion of a generally tubular blank bythe application of fluid pressure within the same. In addition, theforming process may utilize one or more dies having workfacescorresponding to the desired final shape of the article, whethersymmetrical or not, and regardless of variations in the shape orcross-sectior1al area of such article throughout its length. The methoddisclosed herein, as applied to the fabrication of articles frommetallic tubular blanks avoids ballooning or excessive elongation ofmetal in localized areas during deformation of the blank by confiningthe tube within a sleeve which surrounds the outer surface thereof andwhich is gradually withdrawn while a hollow mandrel within the tubularblank supports the inner wall surface thereof and permits theapplication of hydraulic pressure to expand the blank into any one ofvarious complex or intricate shapes determined by the workface contoursof a surrounding die cavity. The outer sleeve surrounding the tubularblank restricts and otherwise limits the expansion of the blank whichwould otherwise occur due to the outward force of hydraulic pressurefrom within its tubular walls. As the stated sleeve is withdrawn fromthe die, force is simultaneously applied radially from within thetubular blank and axially against the end thereof, the effect of whichis to cause deformation of the workpiece progressively along thatportion which is not restrained by the stated sleeve.

One result of the method disclosed herein as referred to above is thatan increase in diameter up to one hundred percent greater than theinitial diameter of the tubular .blank may be achieved with little or nochange in wall thickness of the workpiece. In contrast to this,conventional methods for expanding tubular blanks into finished articlesof bulbous form are successful only in the case of very small diametralexpansion ratios, the precise value of which depends upon the initiallength of the lank considered with the starting wd final diameters ofthe workpiece before and after formation of the finished article.Specifically, the amount which a workpiece of any given metal or alloyin tube or cylindrical form may be successfully expanded by conventionaltube forming devices without resulting in rupture of the workpiece ispartly dependent upon the length of the workpiece over which theexpansion occurs. For example, a ten percent increase in diameter of atubular workpiece of short length may be achieved with relative ease byapplying fluid pressure within the workpiece suificient to force thesides radially outward in all directions an equal amount, whereas thesame diametral ratio of expansion could not be accomplished by thestated method in a workpiece of relatively great length. In the longerworkpiece, application of force from within the tube in an amountsufiicient to exceed the yield strength of the material therein will"ice result in ballooning or local expansion of the workpiece at somerelatively small area along its length, followed by rupture of theworkpiece material at the stated area if the application of radiallyoutward force is continued. Between the two stated extremes there lies aparticular value of length for any given workpiece size, material,condition and expansion ratio which may be termed the critical length,at which expansion under the stated conditions may occur withoutrupture, and which if exceeded will result in localized anduncontrollable ballooning followed by rupture. For example, uniformexpansion of a tubular blank of aluminum to a diameter in excess of fivepercent by conventional means when the critical length is exceeded hasbeen found to result in rupture of the material even with superioruniformity of material composition, thickness and surface smoothness inthe blank before the forming operation is begun.

Accordingly, it is a principal object of the instant invention toprovide improved apparatus for forming tubular blanks into articles ofdiverse shapes having larger area at one or more cross-sectionstherethrough than the stated blank.

It is a further object in the instant case to provide method andapparatus for expanding tubular blanks into various shapes havingnon-uniform cross-sectional size by pressure applied outwardly fromwithin the tube walls.

It is another object of the invention disclosed herein to provide methodand apparatus permitting expansion of tubular blanks to form articleshaving length greater than critical length and cross-sectional sizessubstantially in excess of the cross-sectional size of such blanks.

It is also an object of the invention disclosed herein to provide methodand apparatus as set forth in these objects permitting greaterversatility in the selection of sizes and shapes of finished articlesformed from tubular blanks characterized by the absence of significantchange in wall thickness of the starting blank compared with thefinished article.

it is a further object of the invention disclosed herein to providemethod and apparatus as referred to in the above objects including meansfor forming articles from tubular blanks concerning winch greaterrelative length of the blanks and of the articles may be achieved thanwith devices of the same class known to the prior art.

It is a further object of the invention in this case to provideapparatus for achieving the various objects set forth above by means notrequiring the use of dies, molds or the like.

Other objects and advantages will become apparent upon a close readingof the following detailed description of an illustrative embodiment ofthe inventive concept, reference being had to the accompanying drawings,wherein:

FIGURE 1 shows in side elevation and partly in section, a general viewof apparatus incorporating the inven tive concept disclosed herein,

FIGURE 2 shows an enlarged sectional view, partly broken away, of aportion of the apparatus of FIGURE 1,

FIGURE 3 shows a cross-sectional view corresponding generally to FIGURE2 but with a different shape of die workface, and incorporatingmicroswitch means for con trolling the operation of the apparatus ofFIGURES 13, inclusive.

FIGURE 4 shows a view substantially identical with FIGURE 3 except forthe mieroswitch actuating means in a different operating condition thanthat shown in FIG- URE 3, and

FIGURE 5 shows a general schematic view of the elec trical and hydraulicsystems suitable for use with the apparatus of FIGURES 1-4, inclusive.

With reference to the drawings described above and particularly toFIGURES 1 and 2, a tube forming device incorporating the inventiveconcept disclosed herein is generally designated by reference numeral 1and principally comprises a die portion 16 and a ram portion 12. Whiledie portion may be omitted in "the case of dieless forming as discussedbelow, the apparatus of FIGURE 1 shows an embodiment of the inventiveconcept as applied to die forming. Die portion 10 mainly comprises apair of separable die elements 14 and 16 which may be formed fromsuitable strong and lightweight material such as plastic. Die elements14 and 16 are containedwi hin a two part high strength casing 18 havingflanges 29 whereby the casing elements may be securely held in operativerelationship by appropriate means such as holding bolts 22.

Separable die elements 14 and 16 are shaped to define a cavity 24 formedby workface 26, the contours of which coincide with the desired finalexterior shape of the articles to be formed therein. The ends of cavity24 are designated by reference numerals 28 and 39, which may berelatively far apart as shown by the illustrative examples of FIGURES 1and 2. The stated example also involves a non-uniform variation in thediameter of the cavity 24 as shown by comparison of diameters 32 and 34representing the diameters of two illustrative cross-sections throughthe stated cavity.

The material from which a finished article may be formed is initially ahollow elongate shell such as tubular blank or workpiece 36, one end ofwhich is capped or otherwise closed by appropriate means such as plug 33while the other end remains open. In a manner subsequently described,tubular blank 36 may be deformed so that the initial or startingdiameter of the blank as indicated by reference numeral 49 may beexpanded or otherwise enlarged as indicated by reference numeral 42.Thus, a portion of tubular blank 36 is deformed such as indicated bynumeral 44 progressively along an unrestricted portion of the workpieceupon the application of force thereto.

The amount, the rate, and the location of such progressive deformationis controlled by restricting means including wall supporting means inthe form of outer sleeve 46 surrounding tubular blank 36 and in closeproximity or 7 bearing contact with the workpiece walls about a portionthereof so that no outward deformation or increase in cross-sectionalsize of the blank can occur in that portion contacting outer sleeve 46.Force means for applying force axially upon workpiece 36 are provided inthe form of an inner sleeve 48 situated within outer sleeve 46 andslidable with respect thereto. Inner sleeve 48 is slightly recessed sothat it is not in contact with outer sleeve 46 except at end portion 56of inner sleeve 43, where annular projection 52 is formed as shown byFIGURE 2. Conventional sealing means are provided in the form of annulargroove and O ring means 54 for sealing contact between annularprojection 52 and the inner surface of outer sleeve 46. An edge 56 ofannular projection 52 on inner sleeve 48 abuts the end of tubular blank36 opposite from the closed end thereof.

A hollow mandrel 53 is further provided within inner sleeve 48, by meansof which fluid flowing through conduit means 60 may be conducted to thespace enclosed by tubular blank 36 during the forming operation. Mandrel58 is characterized by a recessed portion 62 of lesser diameter thantubular blank 36, and by a bearing portion 64 at the distal end ofmandrel S8 of slightly larger diameter than recessed portion 62. Bearingportion 64 is sized to provide a sliding fit with the inner surface oftubular blank 36. Passage means 66 communicating between conduit means60 and recessed portion 62 of mandrel 58 permits fluid under pressurewithin the conduit to apply force outwardly upon the walls of tubularblank 36 from within the same, thus avoiding column failure of the blankupon the application of axial loads to the ends thereof as described ingreater detail below.

With specific reference to FIGURE 1, moving means for causing movementof sleeve 46 may be seen to include a conventional flange coupling orjoint 68 by means of which outer sleeve 46 is secured to an hydrauliccylinder 76 at one end thereof. At the endof cylinder '70 opposite fromsleeve 46, the cylinder is closed by a plate element 73 and is affixedby means of a flange coupling 72 to another hydraulic cylinder 74containing a stationary piston '76. Piston rod '78 affixed to piston '76extends through a rod seal 86 and terminates in ball end 82 containedwithin a recess 84 in a stationary end wall 86 and retained therein byplate retention means 88 affixed to wall 86 by suitable means such asbolts 94 Fluid connections 92 and 94 are provided at either end ofcylinder 74 so that, upon pressurization of either side of stationarypiston 76, cylinder 74 and elements connected thereto will be laterallymoved to the left or right as seen in FIGURE 1.

Lateral movement of cylinder 7 4 in the manner referred to above isaccompanied by corresponding movement of cylinder 70 and mandrel 58attached thereto. Independently movable with respect to cylinder "id isa piston d6 contained therein, through the center of which mandrel 58extends. Piston d6 thus constitutes part of the force means for applyingaxial force to workpiece 36 as referred to above. Independent relativemovement of piston 96 with respect to cylinder 70 may be caused bypressurization of cylinder 76 on either side of piston 96 throughappropriate fluid connections 98 and 101 Pressurization within tubularblank 36 may be caused independently and regardless of the pressureconditions in cylinders '70 or 74. Separate conduit means 60 is providedwithin mandrel 58 and communicates in turn through passage 102 toexternal fluid connection 104 at the peripheral edge of flange assembly'72.

Reaction forces due to pressurization of cylinders 70 and '74 andapplied by connecting rod '78 to stationary end wall 86 are opposed bystationary wall 106 through tension beams 108, 110 and 112, whilevertical support for the hydraulic components of ram portion 12 isprovided by a plurality of resilient support elements such asselfcentering hydraulic cylinders 114, 116 and 113 connecting lugs 12%to each of the stated tension beams. It will be understood that otherresilient means such as springs may be used in place of cylinders 114,116 and 118. Casing elements 18 enclosing die means 14 and 16 areaffixed to wall 106 by appropriate means such as bolts 122 and 124 shownin FIGURES 1 and 2.

Referring now to FIGURE 3, tube forming means corresponding generally tothat shown in FIGURES 1 and 2 and discussed above may be seen with theexception of the shape of cavity 124 formed by work-face 126. Moreover,the structure shown by FIGURE 3 includes control means affecting theforming operation as discussed in detail below.

While the total distance between cavity extremities 128 and 130 shown inFIGURE 3, and between extremities 23 and 36 shown, for example, byFIGURE 2, are in both cases substantially greater than the largestcrosssectional diameter of the respective cavities, the cavity shapes ineach case may be seen to differ considerably. Thus, cavity 124 forms aplurality of connecting bulbous or bellows shaped contours adjoining abore 132. Otherwise, the structure of FIGURE 3 corresponds with thatshown and described above in connection with FIGURES 1 and 2. Thus,outer sleeve 146 surrounds a tubular blank 136 in which inner sleeve 148is operatively engaged with abutting edge 156 against the distal end ofthe tubular blank, while mandrel 158 having central conduit means 160therein contacts the inner surface of the workpiece.

In addition to the structure referred to above, outer sleeve 146 isprovided with a collar 209 slidable with respect thereto and normallyprojecting slightly beyond the distal end of the outer sleeve under thebiasing force of spring 208 in the manner shown by FIGURE 3. Collar 2%is provided with a contact screw 202 adjustably 55 mounted on a radiallyprojecting lug 204 and aligned with a microswitch 206 in operativerelationship therewith. Microswitch 2% is connected in circuit withelectrical controls described more particularly in connection withFIGURE 5 below.

As seen from the general schematic view of FIGURE 5 showing anillustrative system adapted for use with the devices of FIGURES 1 to 4,a source of pressure is provided in suitable form such as pump Zltlhaving its outlet connected with conventional pressure modulating meanssuch as accumulator 212. The outlet from accumulator 212 is divided intotwo lines 214 and 216 connected to valves 218 and 220, respectively.Valve 212i is a three-way valve connected to lines 222 and 224communicating with cylinders 76 and 74, respectively. The ends ofcylinders 7t and 74 opposite from the connections of lines 222 and 224thereto, respectively, are connected to valve 22d by means of lines 226and 223. In the position shown, valve 218 connects pressure source 210through line 214% to fluid connection 100 of cylinder 7% and to fluidconnection 94 of cylinder '74, while valve 22% connects the side of eachcylinder opposite from the stated fluid connections to a common drainline 2% communicating with reservoir 248.

While many different conventional items may be used to perform thevarious functions required for operation of the tube forming devicedisclosed herein, the structural details in connection with valve 21%,for example, will serve to illustrate appropriate functionalcharacteristics of the stated control elements without limiting thecontrol system of FIGURE 5 to the precise structural details used toillustrate the same. Thus, valve 213 is shown as being provided witharms 232 and 234 by means of which opposing moments of force may beapplied to valve 218 by link 236 and resilient element 242, respectivelyconnected to the stated arms. Movement of link 235 may be caused bysuitable means such as a solenoid 238 electrically connected in circuitwith microswitch 2% and battery or other power source sea.

It may further be seen from FIGURE 5 that fluid pressure from source 210is connected through lines 216 and 244 with an additional valve 245which also communicates through line 246 to reservoir 248.

Operation The apparatus disclosed herein may be used in forming atremendous variety of diverse articles, and operation of the apparatusmay vary slightly depending upon the shape of the finished article, thedesired final wall thickness or dimensional accuracy of the article, andthe nature or properties of the material in the workpiece. Among thepossible variations in operation, for example, hot forming liquids maybe conducted through conduit 68 to apply fluid pressure for expandingthe article when deformation of the workpiece material will befacilitated thereby. Moreover, the application of forces to a workpiecemay be controlled in their sequence or intensity and coordinated withmovement of sleeves 46 and 48 so that deformation of the workpiece maybe accomplished according to a predetermined schedule without the use ofdies. In addition, beneficial results may be had in forming somearticles by the apparatus of FIGURE 1 except omitting bearing portion64- of mandrel 58. However, operation of the apparatus as shown inFIGURE 1, for example, will be explained in connection with the use ofall the elements shown therein, including dies 14 and 16.

The first step in operating the tube forming apparatus shown by FIGURE 1requires positioning of a tubular blank or workpiece within cavity 24with the tube end nearest die cavity inner extremity 28 plugged orotherwise closed as mentioned above. In the position referred to, outersleeve 45, which is sized according to the requirements of eachparticular forming problem or size of workpiece, is fitted thereover sothat substantially all of workpiece 36 is contained within outer sleeve46 and cir- 5. cumferentially restricted thereby, while a portion of theworkpiece extending beyond the distal end of sleeve 46 remains exposed.Before the forming operation is begun, valve 227 in line 226 may beclosed to prevent passage of fluid in either diretcion through thestated line and valve 218 may be positioned to connect lines 222 and 224with drain line 2349. Thereafter, valve 220 may be positioned to connectlinesc 226 and 228 to pressure line 216 whereby pressure will be appliedat fluid connection 92 of cylinder 74, resulting in the application offorce against plate element 73 to move sleeve 46 toward the left toposition the same with respect to the workpiece substantially as shownin FIGURE 1. With the components of tube forming device 1 positioned inthe required relationship at the beginning of the tube formingoperation, edge 56 of annular projection 52 on inner sleeve 48 contactsthe end of the tubular workpiece opposite from the closed end thereofand is in abutting relationship therewith.

With the various stated elements of device 1 in the startingrelationship described above, the tube forming operation may beinitiated by opening valve 227 and positioning valves 218 and 220 in themanner shown by FIGURE 5. In this position, fluid pressure will beapplied in cylinders 7t) and '74 in a direction resulting in theapplication of force to move cylinder 74 toward the right as shown inFIGURE 1 while piston 76 contained therein remains stationary. Movementof cylinder 7 4 in the stated manner results in simultaneouscorresponding movement of sleeve 46 and mandrel as structurallyconnected thereto. Simultaneously with the application of pressurethrough fluid connection Q4 on cylinder 74, pressure is also appliedthrough line 222 to fluid connection 1% on cylinder 70. The applicationof fluid through connection in the stated manner causes the applicationof force on piston tending to move the piston toward the left as shownin FIGURE 1. During the application of fluid pressure through fluidconnections 94 and 1% as described above, independently operable valve245 may be positioned as shown by FIGURE 5 to cause fluid flow throughconnection ltld and passage 1&2 to conduit 60 within hollow mandrel 53,resulting in the application of force radially outward against the wallsof tubular workpiece 36.

Referring to FIGURE 2, it may be seen that the application of fluidpressure through conduit 60 if sufficiently great may cause deformationof the walls of tubular blank 36 to expand the same. The amount andlocation of such deformation is limited by workface 26 forming cavity 24and further by outer sleeve 46. Thus, before expansion occurs, outwarddeformation of the walls of workpiece 36 in the portion surrounded bysleeve 46 is prevented or otherwise restricted by circumferentialcontact with outer sleeve 46, whereas after expansion occurs in anamount suflicient for the walls of workpiece 36 to contact workface 26of cavity 24, further deformation is prevented by the stated Workfacesurfaces. In consequence of the stated restriction effects, portion 44of workpiece 36 shown in FIGURE 2 is an area of local deformation whichmoves progressively and in a plurality of separate adjoining incrementsalong the entire length of cavity 24 as sleeve 46 is withdrawn.

Due to the structural relationship of parts in the apparatus disclosedherein and the functional results obtained therefrom as discussed above,it will be understood that the application of pressure through fluidconnection 94 to cylinder 74 to withdraw sleeve 46 during the formingoperation is accompanied by the application of pressure through fluidconnection 1% of cylinder 70 applying force to piston 96, and that theforce thus applied to piston 96 is transmitted through inner sleeve 48and abutting edge 56 to workpiece 36. As detailed below, the statedforce applied by abutting edge 56 is used to cause movement of thetubular workpiece longitudinally toward the left as shown in FIGURE 2.

The effect of the forces applied to workpiece 36 as a result of theoperations described above causes deformation of the workpiece materialto form an article having an external shape coinciding with the contoursof workface 2,6. The stated deformation begins with the simultaneous aplication of force due to fluid pressure within workpiece 36 and endwiseby projecting edge 56 causing movement of workpiece material toward theleft as shown in FIGURE 2, for example. Thus, excessive localdeformation of the workpiece material due to expansion of the workpiecediameter is avoided by reason of the continuous addition of suchmaterial by movement of inner sleeve 48 toward the left in FIGURE 2.Simultaneous with the application of radial force due to fluid pressurewithin workpiece 3d and endwise force on the workpiece material due toleftward movement of inner sleeve 48, outer sleeve 46 is graduallywithdrawn so that deformation of the workpiece material occurs only inthe portion thereof which is nearest the distal end of the outer sleeve.Thus, deformation is localized and occurs only in a narrow incrementalong the workpiece length, the number and size of such incrementsdepending upon the movement of sleeve 45.

The amount of force required in each case and the rate of movement ofeach stated element acting on workpiece 36 may be varied to produce thebest results depending upon the factors involved in each particularforming problem. For example, the force sutlicient to expand thediameter of workpiece 3d obviously depends upon that required to exceedthe yield strength of the workpiece material. Similarly, variations inthe rate of'moven'i nt of the movable parts discussed above may occurwithin a wide range depending on the Shape of workr'ace as as well asthe extent of dimensional change involved in the comparison of initialand final workpiece sizes. For example, orifices 25 and 252 are shown asa possible means for controlling the relative response of cylinders Illand '74 according to a desired relationship between their respectivemovements.

' In any case, it is of utmost importance in practicing the inventiveapparatus and method disclosed herein that outer sleeve 46 is initiallypositioned in close proximity to the walls of workpiece 36 and preventsthe application of fluid pressure within the workpiece from deformingthat portion of the workpiece wln'ch may contact the sleeve. Similarly,it is of further and equally crucial importance that deformation of theworkpiece material occurs in a controlled and localized areaprogressively throughout substantially the entire length of theworkpiece, starting at or near the closed end thereof and thereaftermoving toward the distal or open end of the workpiece during carefullycoordinated movement of sleeves 46, 48, mandrel 58, and simultaneousapplication of pressure in a predetermined amount through conduit 69.From the description of structure and operation of the same as discussedabove, it will be understood that the action of outer sleeve 46 inFIGURE 2, for example, during coordinated movement of inner sleeve 4%provides control of the amount and rate of deformation occuring at anymoment of time during the tube forming operation. Thus, localdeformation of the workpiece material occurs only when or as permittedby movement of the apparatus parts which apply force to the workpiece asdetailed herein, and cannot occur at unpredictable or uncontrolled timesand locations such as characteristic of conventional devices forexpansion forming of large articles from tubular blanks. Even duringdieless forming as referred to above, the location and amount ofdeformation can be accurately controlled by coordinated movements of aplug-type mandrel having a closed tip and otherwise similar to mandrel58 but axially movable with respect to outer sleeve 45.

While various controls or programming devices for coordinating orcontrolling the forces applied on workpiece 36 and the amount or rate ofmandrel and sleeve movements discussed above will occur to those skilledin the art, the scope of the teachings herein is not limited by theselection of any particular controls or regulating devices. Accordingly,use of microswitch 2% and associated structure is disclosed'herein asmerely illustrative of one type of control. From the description setforth above relating to collar Zilli shown in FIGURE 3, for example, itmay be seen that the deforming portion 44 of workpiece 136 has acharacteristic curvature, the precise contours of which depend upon theamount of deformation in the stated material which occurs while outersleeve 146 remains in any given position. When pressure is continuouslyapplied radially outward against the walls of tubular workpiece 136, thecharacteristic shape of deforming portion .44 causes the workpiecematerial to contact the edge of collar 200 as shown by FIGURE 4, afterwhich continued pressure applied in the stated manner causes movement ofdeforming portion 44 to move collar 2% toward the right as viewed inFIGURES 3 and4 whereby contact screw ZilZ causes actuation ofmicroswitch 2%. Actuation of microswitch 2% may cause momentarypositioning of valves 213 to apply pressure from source are to cylinders7i? and 74. Upon application of pressure to cylinder 74 outer sleeve 146will move toward the right as viewed in FIGURE 3 by amount dependingupon the pressure applied within cylinder 74 and the period of timeduring which it is applied. Movement of outer sleeve 146 and collar 2%mounted thereon toward the right will separate collar 2% y fromdeforming portion 4a of workpiece 136, permitting spring 2% to movecollar Ziltl toward the left with respect to outer sleeve 14%, thusreleasing microswitch 2636 and dcenergizing solenoid 233. When solenoid238 is deenergized, return spring 242 may alter the position of valve218 to close the same and prevent the application of pressure tocylinders 7th and '74. Thus, outer sleeve 146 may remain in the positionwith respect to workpiece 136 which it had at the time that spring 242causes valve 218 to close, and to maintain substantially the sameposition until further deformation of workpiece material causes movementof collar 2M? and again actuates microswitch 206. In the stated manner,automatic and progressive forming of an article within cavity 24 mayoccur in gradual stages proceeding from one end to the other of thestated cavity.

In addition to the cavity shapes shown by FIGURES 1-4, the inventiveconcept disclosed herein is useful in fabricating objects of manydifferent types, materials and shapes, including arcuate or curvedtubular ducts and the like. Moreover, many shapes may be achieved byprogramming the amount or rate of movement of sleeves 46, 4t; andpressures applied through conduit 60 even without the use of dieelements 14 and 16 or other workface element, according to the processreferred to in the art as dieless forming. However, when dies are usedin the novel process herein disclosed, it is characteristic of the tubeforming process taught herein that the workpiece material as it expandsto the utmost limit permitted by workface 26 in cavity 24 of FIGURE 1,for example, will guide or control the direction of sleeves 46 and 43and the movable parts of device 1 associated therewith. In order toprovide freedom of directional movement of that portion of tubularworkpiece 36 contained within outer sleeve 46, together with the sleeveitself and associated parts, ram portion 12 is mounted on ball end connection 82. at one extremity and supported by resilient means 134, 116and 118 near the other extremity as described above. Moreover, the endof cavity 24 into which sleeves 46 and 48 initially project may beoversized as in the case of bore 132 shown in FIGURE 3, to permit alimited range of directional movement of the stated sleeves andassociated parts with respect to stationary die portion it). Thismovement permits the deformation of the workpiece, as affected by thecontours of workface 26, to vary the position of sleeves 46, 48, mandrel58, and other parts supported by resilient means 114, 116,

and 118 continuously if necessary throughout the forming operation.

The tube forming method and apparatus taught herein avoids the extremelysevere limitations associated with conventional tube forming techniqueswell known to those skilled in the art. For example, the formation of anarticle in the final shape corresponding to cavity 24 shown in FIGURE 2starting with a metallic tubular blank of the relative size shown by thestated figure using conventional method and apparatus could only resultin excessive local elongation of the workpiece material in anunpredictable area followed inevitably by rupture of the same longbefore the final diameter of the finished part could be achieved. Thus,if radial force were applied from within the tubular blank by hydraulicpressure without the action of outer sleeve 46 in FIGURE 2, for example,expansion of the workpiece would not be uniform throughout eachincrement of its length, but the amount and rate of expansion would varywith each variation in unit strength and wall thickness at eachincrement. If the material thickness were not absolutely uniform andconstant, the relative weakness of the workpiece at the locations ofleast wall thickness would result in local expansion at such locationsin excess of that occurring elsewhere throughout the workpiece. In viewof the normal practical manufacturing tolerances involved in industry,minute variations in wall thickness occurring in the average initialworkpiece or tubular blank are sufficient to render expansion-forming ofarticles of greater than critical length totally impractical from aneconomic and design standpoint. Small or relatively short objects suchas door knobs, for example, are commonly formed within die cavities bythe application of hydraulic force from within and longitudinal forceapplied by mechanical means to the end of the tubular blank, but thestated technique is unworkable in the fabrication of larger objectshaving significantly greater length than that which characterizes doorknobs and the like.

In contrast to the limitations of conventional tube forming techniquesas referred to above, the invention disclosed herein provides severaladvantages and results not achieved previously in the art, and has beensuccessfully used in forming objects 36 inches long, but could be usedfor objects of even greater length. The optimum choice of fabricationmethod based upon considerations such as weight, reliability and cost isprovided by the teachings contained herein. Thus, for example, ducting,bellows members, elongate tanks or other fluid containing elements maybe fabricated in the manner described above to provide one-piece,accurately formed parts of complex shape and uniform wall thicknessthroughout the finished part having final diameters as much as onehundred percent greater than the initial diameter of the tubular blankfrom which the part is formed. The cost of fabrication usin' theteachings set forth above are considerably less than those involved inthe fabrication of similar parts by conventional methods. For example,one orthodox approach in the fabrication of large, relativelythin-walled components of complex shape is to fabricate the part fromindividual sections which are separately formed and thereafter weldedtogether along a plurality of seams. In addition to avoiding theincreased cost of various joining methods incident to fabrication of apart in two or more separate pieces, the tube forming method andapparatus disclosed herein reduces tooling costs by the use of plasticmaterial in separable die elements M and 16, or in eliminating thenecessity for dies if the desired final shape of the article permitsdieless forming of the same. Where dies are used such as shown at 14 and16 in performing the process taught herein, they are subjected only tocompression and are not required to possess high strength properties orsurface hardness such as characteristics of forging dies, for example,since die elements 14 and 16 do not deform the workpiece material butmerely limit or otherwise restrain the amount of deformation occurringby reason of the forces applied mechanically and hydraulically asdescribed above.

While the particular structural details set forth above and in thedrawings are fully capable of attaining the objects and providing theadvantages herein stated, the structure thus disclosed is merelyillustrative and could be varied or modified to produce the same resultwithout departing from the scope of the inventive concept as defined inthe appended claims.

I claim:

1. In apparatus for forming a hollow article by expansion forming of agenerally elongate hollow rigid blank of deformable material; die meansincluding a die cavity of generally elongate shape, at one extremity ofwhich said blank is adapted to be supported by said die means while theremainder of said blank is unsupported by said die means within saidcavity, the length of said die cavity being substantially in excess ofthe critical length for said material with respect to the amount of saidexpansion, fluid pressure means for filling the interior of said blankwith fluid under pressure whereby outwardly direct force is appliedwithin said blank to expand the same, restricting meanscircumferentially contacting a portion of the outer surface of saidblank whereby expansion of said portion is initially prevented duringapplication of said outward force, moving means for moving saidrestricting means relative to said blank during application of saidforce whereby the material in said portion is gradually exposed andthereby permitted to expand, said expansion occurring progressively bysuccessive deformation of said material in a plurality of increments aseach increment of said surface is exposed by movement of saidrestricting means by said moving means, and force means for applyingforce axially to displace said portion simultaneously with movement ofsaid restricting means and in a direction opposite to said movement.

2. The method of forming a hollow article from a rigid shell blankhaving an open end and a closed end, said method comprising: positioningwall supporting means in close juxtaposition with a first portion of theexterior surface of said blank while a second portion thereof isexposed, applying outwardly directed force to the interior surface ofsaid blank, simultaneously applying axially directed force on the openend of said blank to displace said first portion thereof along agenerally linear path, and during the application of said forces, movingsaid wall supporting means with respect to said blank in a directionopposite to the direction of said displacement to gradually expose saidfirst portion whereby deformation of said blank occurs progressivelystarting with said second portion and continuing by progressiveincrements along the length of said blank as said first portion isexposed by said movement of said wall supporting means.

3. The method of forming a hollow article from an elongate rigid tubularshell blank having an open end and a closed end, including: placing saidblank in a die with said closed end rigidly supported by said die andthe remaining length of said blank unsupported by said die, positioninga mandrel within said blank and axially aligned therewith, extending asleeve over a portion of said unsupported length of said blank with saidsleeve in axial alignment therewith and in slidable contact with theouter surface of said blank, filling said blank with fluid undersufficient pressure to deform the walls thereof, thereafter retractingsaid sleeve thereby permitting said blank to deform progressivelyproceeding incrementally along the length of said blank as said sleeveis retracted during the application of said fluid pressure, and applyingaxial force to displace said portion in a direction opposite to themovement of said sleeve during retraction thereof, said displacementoccurring simultaneously with said movement and operatively coordinatedtherewith.

4. In apparatus for forming a hollow article from an elongate shellblank of deformable metallic material; fluid pressure means for fillingthe interior of said blank with fluid under pressure whereby outwardlydirected l l a force is applied to the wails of said blank to deform thesame, restricting means positioned in close proximity to a portion ofsaid Walls exteriorly thereof whereby deformation of said portion isinitially prevented during application of said outward force, movingmeans for moving said restricting means relative to said blank duringapplication of said force whereby the material in said portion isgradually exposed and thereby permitted to deform, said deformationoccurring progressively and coincidentally with the movement of saidrestricting means by said moving means, and force means for applyingforce axially to displace said portion simultaneously with movement ofsaid restricting means and in a direction opposite to said movement,said restricting means including an elongate hollow member adapted tosurround said portion in sliding contact with the walls of said blank,said blank being cylindrical with one end closed and the other endopened, said elongate hollow member being an outer sleeve havingcomplete circumferential contact with said portion and sized to providea sliding fit therewith, said force means including an inner sleeveconcentrically located Within said outer sleeve and axially movable withrespect thereto, said inner sleeve having an annular projection adaptedto contact said open end of said blank in abutting relationshiptherewith.

5. The apparatus set forth in claim 4 above in which said fluid pressuremeans includes a hollow mandrel having conduit means therein throughwhich said fluid may be flowed into the interior of said blank to fillthe same.

6. The apparatus set forth in claim 5 above in which said mandrel has alesser diameter than the interior surface of said walls whereby fluidpressure holds said Walls against internal collapse.

7. The apparatus set forth in claim 6 above including in additionthereto, a workface for limiting the amount of expansion of said wallswhereby the shape of said article is made to coincide with the contoursof said workface.

8. In apparatus for forming a hollow article from an elongate shellblank of deformable metallic material; fluid pressure means for fillingthe interior of said blank with fluid under pressure whereby outwardlydirected force is applied to the walls of said blank to deform the same,restricting means positioned in close proximity to a portion of saidwalls exteriorly thereof whereby defor-.

mation of said portion is initially prevented during application of saidoutward force, moving means for moving said restricting means relativeto said. blank during application of said force whereby the material insaid portion is gradually exposed and thereby permitted to deform, saiddeformation occurring progressively and coincidentally with the movementof said restricting means by said moving means, force means for applyingforce axially to displace said portion simultaneously with movement ofsaid restricting means and in a direction opposite to said movement, anda Workface adapted to limit the amount of deformation of said wallswhereby the shape of said article is made to coincide withthe contoursof said workface, said blank being initially cylindrical, saidrestricting means including an outer sleeve in sliding contact with saidportion of said blank, and said force means including an inner sleeveconcentrically located within said outer sleeve.

9. The apparatus set forth in claim 8 above, including in additionthereto, control means for coordinating said movements of saidrestricting means and said force means according to a predeterminedschedule to vary the shape of said article produced by said deformation.

10. In apparatus for forming a hollow article from an elongate shellblank of deformable metallic material; fiuid pressure means for fillingthe interior of said blank with fluid under pressure whereby outwardlydirected force is applied to the walls of said blank to deform the same,restricting means positioned in close proximity to a portion of saidwalls exteriorly thereof'whereby deformation of said portion isinitially prevented during application of said outward force, movingmeans for moving said restricting means relative to said blank duringapplication of said force whereby the material in said portion isgradually exposed and thereby permitted to deform, said deformationoccurring progressively and coincidentally with the movement of saidrestricting means by said moving means, force means for applying forceaxially to displace said portion simultaneously with movement of saidrestricting means and in a direction opposite to said movements, saidrestricting means including a sleeve in which said workpiece slidablyfits with the external surface of said portion in contact with theinternal surface of said sleeve while the remaining portion of saidworkpiece projects beyond the distal end of said sleeve, and saidapparatus further includes control means for coordinating said movementof said restricting means and said displacement of said force meansaccording to a predetermined schedule to vary the shape of said articleproduced by said deformation, die means including a die containing acavity with a bore communicating said cavity with the external diesurface, said sleeve being adapted to project into said cavity throughsaid bore, said sleeve being universally mounted to permit angularvariations in the position of said sleeve with respect to said dieduring said deformation, and said bore being larger in cross-sectionalarea than said sleeve to permit said variations.

11. The structure set forth in claim 10 above in which said moving meansincludes hydraulic force means comprising a cylinder for moving saidsleeve upon the application of said hydraulic pressure within saidcylinder, a source of fluid pressure, and connecting means between saidcylinder and said source, said force means including an abutting memberadapted to contact the open end of said blank, a hydraulic pistonoperatively associated with said abutting member whereby axial force isapplied to said workpiece upon the application of fluid pressure to saidpiston, and connecting means between said piston and said source adaptedto apply pressure to said piston.

12. The apparatus set forth in claim 11 above in which said controlmeans includes a movable element slidably mounted on said sleeve, amicroswitch mounted on said sleeve and operatively associated with saidmovable element whereby intermittent movement of said movable ReferencesCited in the file of this patent UNITED STATES PATENTS 2,288,454- HobsonJune 30, 1942

1. IN APPARATUS FOR FORMING A HOLLOW ARTICLE BY EXPANSION FORMING OF AGENERALLY ELONGATE HOLLOW RIGID BLANK OF DEFORMABLE MATERIAL; DIE MEANSINCLUDING A DIE CAVITY OF GENERALLY ELONGATE SHAPE, AT ONE EXTREMITY OFWHICH SAID BLANK IS ADAPTED TO BE SUPPORTED BY SAID DIE MEANS WHILE THEREMAINDER OF SAID BLANK IS UNSUPPORTED BY SAID DIE MEANS WITHIN SAIDCAVITY, THE LENGTH OF SAID DIE CAVITY BEING SUBSTANTIALLY IN EXCESS OFTHE CRITICAL LENGTH FOR SAID MATERIAL WITH RESPECT TO THE AMOUNT OF SAIDEXPANSION, FLUID PRESSURE MEANS FOR FILLING THE INTERIOR OF SAID BLANKWITH FLUID UNDER PRESSURE WHEREBY OUTWARDLY DIRECT FORCE IS APPLIEDWITHIN SAID BLANK TO EXPAND THE SAME, RESTRICTING MEANSCIRCUMFERENTIALLY CONTACTING A PORTION OF THE OUTER SURFACE OF SAIDBLANK WHEREBY EXPANSION OF SAID PORTION IS INITIALLY PREVENTED DURINGAPPLICATION OF SAID OUTWARD FORCE, MOVING MEANS FOR MOVING SAIDRESTRICTING MEANS RELATIVE TO SAID BLANK DURING APPLICATION OF SAIDFORCE WHEREBY THE MATERIAL IN SAID PORTION IS GRADUALLY EXPOSED ANDTHEREBY PERMITTED TO EXPAND, SAID EXPANSION OCCURING PROGRESSIVELY BYSUCCESSIVE DEFORMATION OF SAID MATERIAL IS A PLURALITY OF INCREMENTS ASEACH INCREMENT OF SAID SURFACE IS EXPOSED BY MOVEMENT OF SAIDRESTRICTING MEANS BY SAID MOVING MEANS, AND FORCE MEANS FOR APPLYINGFORCE AXIALLY TO DISPLACE SAID PORTION SIMULTANEOUSLY WITH MOVEMENT OFSAID RESTRICTING MEANS AND IN A DIRECTION OPPOSITE TO SAID MOVEMENT.